1. Field of the Invention
Embodiments of the present general inventive concept relate to an image forming apparatus and an auto color registration method thereof, which perform an auto color registration operation by excluding or minimizing the influence caused by variation in speed of a drive roller driving a transfer member.
2. Description of the Related Art
Generally, an image forming apparatus has been widely used to print an image on a printing medium such as paper according to an input image signal. There are a variety of image forming apparatuses, for example, a printer, a copier, a facsimile, and a combination thereof such as a multi-functional printer.
For example, an electrophotographic-type color-image forming apparatus may be a tandem-type image forming apparatus. The tandem-type image forming apparatus includes as many photo-conductors as the number of colors used for printing and as many developing machines as the number of colors used for printing.
Generally, the color image forming apparatus uses toners of four colors (Yellow, Magenta, Cyan, Black), such that the tandem-type image forming apparatus includes four photo-conductors corresponding to individual colors and four developing machines corresponding to the individual colors. This image forming apparatus is able to print data at high speeds, but it performs the color printing by overlapping images of the individual colors on individual photo-conductors, such that a defective image caused by a color registration error may easily be generated.
Accordingly, the color image forming apparatus performs an auto-color registration (ACR) operation to accurately arrange individual colors at desired positions of the paper.
The ACR operation may be used to correct a relative position where four colors are formed in such a manner that images of four colors are correctly arranged on the paper. Typically, according to the ACR operation, test patterns of respective colors are sequentially printed on the printing medium one by one, and the interval between test patterns of respective colors is detected, such that distortion, i.e., a color registration error, may be corrected according to the detected result. By the above ACR process, image quality may be increased.
However, the conventional image forming apparatus has performed the ACR process without considering a mechanical variation factor caused by the drive roller. Although the variation in speed occurs according to the shape of the drive roller which drives the transfer member to transfer the printing medium onto which the test pattern is printed, the conventional image forming apparatus does not prepare for color image distortion caused by the variation in speed of the drive unit, such that precision of the ACR operation is unavoidably decreased, resulting in a deterioration of image quality.